1. Field of the Invention
The present invention relates to a recording apparatus for use in, e.g., a copying machine, a facsimile system, a video output printer, and a word processor and, more particularly, to an ink quantity detecting device of a recording apparatus using different types of ink.
2. Related Background Art
Recording apparatuses such as a printer or a facsimile apparatus can be classified in accordance with a recording system into, e.g., a thermal system, a wire dot system, and an ink jet system.
In the ink jet system (ink jet recording apparatus), an ink is supplied to a recording head having at least one small orifice as a discharge port, and an energy generator provided in correspondence with the orifice is driven on the basis of printing data, thereby forming bubbles by a film boiling phenomenon of the ink in the orifice. Ink droplets are ejected from the orifice upon expansion and shrinkage of the bubbles, and the ejected ink droplets are adhered on a recording member such as plain paper or a thin plastic plate, thereby forming dot patterns.
In an ink jet recording apparatus of this type, an ink is supplied to the recording head from an ink container called an ink tank or an ink cartridge mounted in the apparatus or a carriage via a tube or the like. Since the ink capacity of the ink container is limited, however, the supply of ink remaining becomes small to interfere with subsequent recording when a recording operation progresses to a certain degree. Therefore, the apparatus is arranged such that a decrease in the supply of the ink remaining to a reference quantity is detected by a certain method to alarm an operator before the ink is used up, thereby demanding the operator to replenish the ink or replace the cartridge.
An optical system or an electrode system is conventionally known as a typical ink quantity detecting means for an ink container. The optical system is suitable for an arrangement in which the ink container has a surface which can be opened by a cover. In the optical system, a detection signal is generated by utilizing an event in which light emitted from a light-emitting portion reaches a light-receiving portion when the ink liquid surface is lowered. In the electrode system, a pair of electrodes are horizontally arranged near a predetermined liquid surface level with a predetermined interval therebetween, and a signal is generated by utilizing an event in which an electric resistance abruptly rises when the electrodes are exposed to the air.
In addition to the above systems, a pressure detecting system is available. In the pressure detecting system, a pressure sensor is arranged in an ink bag such as an aluminum laminated bag, and the supply of ink remaining is detected on the basis of a pressure change.
The present inventors found, however, that when such an ink quantity detecting device is applied to a recording apparatus using at least two different types of ink, the following technical problems to be solved arise.
For example, U.S. Pat. No. 4,719,475 discloses an arrangement in which electrodes arranged in a plurality of ink tanks are connected in series with each other to detect an ink quantity.
Japanese Laid-Open Patent Application No. 60-32667 discloses an arrangement in which light is radiated on a transparent portion formed in an ink tank and a quantity and a color of light transmitted through a light guide are observed to detect an ink quantity.
In each of the above conventional ink container ink quantity detecting devices, however, if the optical system or the electrode system is used as the detecting means, the stability of ink may be degraded over a long time period, i.e., the quality of ink may be degraded especially when the ink is left to stand at a high temperature.
In this case, the quality of an image is degraded when recording is performed in a color recording apparatus for a long time.
Especially in the above arrangement in which electrodes are connected in series with each other, in order to select a resistance range which can be sensitively detected, a voltage must be increased since resistive components are increased due to an ink. As a result, the above-mentioned influence on the ink is enhanced.
The pressure detecting system has no influence on ink performance. However, if a pressure sensor is arranged for each color in order to apply the system to a color recording apparatus, the size of the apparatus is increased, and manufacturing cost of additional mechanisms is increased.